Human beings can use only a small fraction of Earth’s water. In school, we were taught that most (specifically, 71 percent) of the planet’s surface is covered in water. While that’s true, humans can use only 0.007 percent of that water, according to National Geographic. That’s because only about 2.5 percent of Earth’s water is fresh water, and only 1 percent of that is accessible. The rest makes up glaciers and snowfields.